feat(css): deprecate css default export

[bluwy]

Description

Supersedes and closes #10762 (See for more context)

This PR adds on top of #10762, including:

• Warn of default import of css through import analysis (dev only)
• Warn globbing default import of css through glob plugin
• Update CSS test. Default imports of CSS does not work with HMR.

Additional context

I got flaky sourcemap test failures locally and I'm not sure if it happens in CI too

example fail log

 FAIL  playground/css-sourcemap/__tests__/css-sourcemap.spec.ts > serve > linked css with import
SyntaxError: Unexpected end of JSON input
 ❯ new Converter node_modules/.pnpm/convert-source-map@1.9.0/node_modules/convert-source-map/index.js:70:48
     68|   if (opts.hasComment) sm = stripComment(sm);
     69|   if (opts.isEncoded) sm = decodeBase64(sm);
     70|   if (opts.isJSON || opts.isEncoded) sm = JSON.parse(sm);
       |                                                ^
     71| 
     72|   this.sourcemap = sm;
 ❯ Proxy.exports.fromComment node_modules/.pnpm/convert-source-map@1.9.0/node_modules/convert-source-map/index.js:149:10
 ❯ Module.extractSourcemap playground/test-utils.ts:291:10
 ❯ playground/css-sourcemap/__tests__/css-sourcemap.spec.ts:68:17

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.